Process for the manufacture of titanium-aluminum alloys and regeneration of intermediates



United States Patent 2,781,261 PROCESS FOR THE MANUFACTURE or TITA- ALIDYS REGEN- ERATION OF TERMEDIATES Jonas .Kam let, Easton, -Conn., assignorto National Distillers Products Corporation, New York, N. Y., a .corpora'tion of Virginia No Drawing. Application October 30, 1953,

SriaL-No. 389,503

intermediates of said process. .More .particular-.ly,zit relates to process forzthe manufacture of titanium-aluminum R 2,781,261 Hcg I Patented Feb. 12, 1957 2 titanium comprise simple solutions of the aluminum in the titanium and do not form intermetallic compounds. Formation of alloys containing up to 75% of titanium proceeds .ata rapid rate. As a rule, the more aluminum that is-used (within the limits above described), the more alloys containing from 0.1% -to -9'5% 0T titanium, and for the processing of the by-products of said process to regencrate the intermediate chemical compounds required for the manufacture sofssaid alloys.

v .Manchot and Richter (Annalen.357., 140-144 (1907)) reacted .potassium .fiuotitanate with metallic aluminum in .quantity .fiar .in:stoichiometric excess of that required by the equation:

3K2TiFs 4Al 2K3A1Fs 2A1F3+3Ti at advanced temperatures, andvdbtai'ned -a titanium-aluminum alloy containing 9.4% of titanium. In my copending application Serial No. 882,206, I hav'e shown "that alloys containing from 58 to 95% of titaiiium (the remain'der being aluminum) may be "obtained by the reaction, at advanced temperatures, of alkali metal fiuotitanates with aluminum in quantities within a closely specified range. *I mow "find that a'lloys of titanium and aluminum containing from 0.1%"to"95 oftitanium can be obtain'e'd hy the ireaction, at advanced itemperatures, of a'lkali metal fluotitanates with metallic aluniinumyem- *p'loying per gram-mo le'of alkali metal fiuotitanate (i. e. per 207.9 grams of NazTiFe, or per 17528' grams of *LiTiFs, or per 240.1 grams-'oFKaTiFs from'385grams 10 47. 9 kilograms dfmetallicaluminum.

This veiy broad range "of titanium contents *in :the alloys obtained requires somewhat-different modes 'of operating, depending won the melting point of the alloy to be prepared. The followingichart represents the approximate-meltingpointiof the series of .alloys'tpreparable bythe process of this invention:

. tBinarywall'oys containing "up "to 37.28% :of 'titaniumcon-c sist of crystals-of 'titaniumialuminide '(TiAh) dispersed -in=:excess:-aluminum. iFheibimiryalloy containing 37.28%

of titanium COI'I'6PIOIIdS"tO.miAb.lilLdOInPlOSitlOn. Binary :alloys containing-137128 75 ito 53% of titanium consist of rapidand-complete-isthe reactionbetweenthe alkali metal fiuotitanate and the aluminum, and the formation of the titanium-aluminum alloy. As the amount of aluminum is decreased, the reactionwith the alkali-metal fluotitanate becomes slower, and there is a greater tendencyfor incomplete reduction of the alkali metal fluotitanate'with formation of divalent and trivalent titanium compounds. -By ,prolonged heating, however, alloys containing up to 95% titanium may however be obtained by this method.

The temperatures at which-this reaction may be efiected may vary quite widely. .It is desirable to have atleast one ofthe reagents (i. e. the aluminum.) in a molten state, 'and'prcferably both the aluminum and 'thealkali jmetahfluotitanatesshould be in amoltenstate. Thus, the

lower limitoftemper'ature for this reaction'isiset by the *meltingp'oint of aluminum, i. 'e.;660 C. Both reagents are molten in the range of 900 1100 C. The upper limit of temperaturetor'this reaction is setby the boiling point .of aluminum (1800 C.) and the melting point of the .alloy .being prepared. It is desirable, at the conclus'ion'of Ithe reaction, to be .able to separate a molten regulus of titanium-aluminum alloy'frornthe concomitant slag consisting of molten alkali metal aluminum fluoride and aluminum "fluoride. -Thus, the temperature range for'this rea-ction'm'aybe given as 660 C. to 1800' C., with a preferredrange between11(l0 C. and 1750 0., depending on the compositionfdf the alloy being prepared.

.A,preferred.method .for effecting this. stepof the. inventioniisdomixthe calculated .quantityof molten aluminum and. alkali metal fluotitanate in a refractoryrlined crutwo molten alaye'rs are then separated by decantation, in

- 'theulsual manner,- andteach is then allowed to cool slowly --ct yst'als of tit'aniumalumini'de dispersed in excesstitanium "metal. Binary alloys containing from 53%. to of and'solidify. =Magnesia-lined crucibles are,as a-rule,-suitable for the eflecting of the reaction of this invention "-since they are not excessively attacked atthe indicated reaction temperatures.

Although some of the alkali .metal fluotitanates are "knowntto form crystallinehydrates at. lowertemperatures, they-are, of acourse,=employed as anhydrous salts atthe temperature rangesinvolved in 'ther'process of this invention. Since thealuminum is always employed in "the molten state it need not belcomminuted priorto addition to the reaction mixture, but' may be added :to the-cru- -cible as bar or-pig'aluminumor in the molten state.

ilhe titanium-aluminum .alloys thus prepared-have a Wide range of-utilityin industrial metallurgy. They are er'nployedtorefine-grain structure, remove gas occlusions,

increase tensile: strengths, increase resistance to leaking of castings, rimprove' mechanical properties, decrease the electrical conductivity, increase impact resistance, n-

crease resistance to acids, saline and Eother aggressive solutions,=increase corrosion resistance, improve castings and lower the casting-temperatures of various metals and alloys loui'ufil'nsn-Metals 1930, '53 1,-Chema-Zintr. 1937i, 2002; 19441, 242; Allumino 16,?5 l-947-).;:.U. S. Patents 2,252,421 and 2,376,681; Metallurstschaft 21, 683 (1942) Chimie & Industrie 26,338 *(1932); Aluminium 17, 79 (1934); 49,635 (1937:); .20,- 452"(.1 9 38) 26, 2 (1944); British Patent 473,916; Zeit. -Anor-g. Chem. 150, 26

B Trans. 1143 (1951).

e r 2,781,261 a p s In my co-pending patent application Serial No. 382,206, I also describe the use of alloys of titanium and aluminum containing from 53% to 95% of aluminum as intermediates in a process for the manufacture of titanium metal.

The by-product mixture of molten salts obtained with these titanium-aluminum alloys consists of substantially equimolecular proportions of alkali metal fluoaluminate (MsAlFs) and aluminum fluoride. Since the starting material-the alkali metal fluotitanate-is not a common article of commerce, it is a further purpose of this invention to provide a simple process for the conversion of this by-product mixture of MsAlFs and AlFs to the original starting material, i. e. the alkali metal fluotitanateM2TiFe.

I have found that this regeneration of the alkali metal fluotitanates may be effected by the following sequence of steps:

STEP A The molten slag, comprising a substantially equimolecular mixture of alkali metal fluoaluminate and aluminum fluoride, obtained as above described, is cooled, comminuted and added to an aqueous slurry of milk of lime. The lime is used in stoichiometric proportions according to the equation:

(where M is an equivalent of an alkali metal), the- STEP B The solution of alkali metal aluminates is then treated with a carbon dioxide-containing gas, until precipitation of aluminum hydroxide is complete, according to the equations:

This carbonation may be effected at ordinary or advanced temperatures and at atmospheric or superatmospheric pressures, according to the well known procedures of the art. The precipitate of aluminum hydroxide is then filtered or centrifuged from the aqueous solution of alkali metal carbonate (which may contain some bicarbonate when overcarbonated). The aluminum hydroxide may then be calcined (e. g. at 1000 C.) and converted to alpha-alumina for use in the electrolytic aluminum process. Alternatively, it may be used in the manufacture of alum, aluminum chloride or other aluminum salts.

In my co-pending patent application covering a process for the manufacture of titanium metal, I obtain a byproduct of alkali metal aluminate solution by the selective leaching of the aluminum from a titanium-aluminum alloy of specified composition. This by-product alkali metal aluminate solution may be mixed with the alkali metal aluminate solution obtained as a filtrate in Step A, and the combined solutions carbonated togetherto recover aluminum hydroxide and alkali metal carbonate solution. Thus, all of the aluminum used in this process is ultimately recoverable as aluminum hydroxide or alpha-alumina. If purer by-product CO2 gas is not available, filtered flue gas free of H28 and 802 may be used for the above-described carbonation.

' STEP The calcium fluoride precipitate obtained in Step A above is reacted with sulfuric acid, according to any of the procedures well known to the art, to produce hydrogen fluoride. Thus, for example, a mixture of the calcium fluoride precipitate and 66 B. sulfuric acid arefed into a rotating retort in theproportions of 1 mole of CaFz per 1.3-1.5 moles of H2504. The rotating retort is fired by gas or oil, and at the feed end, hydrogen fluoride gas is withdrawn at a temperature of 120 C.l C. The gases pass through a dust collector (to remove fine particles of CaFz carried over) and thence are drawn into a series of absorption towers where the HP is dissolved in an aqueous medium to obtain aqueous hydrofluoric acid solutions of 5% to 52% HF concentration, although more concentrated solutions may be obtained by recirculation. For the process of this invention, solutions containing 5% to 50% of HF, made from CaFz and H2804 by any of the processes of the art, are suitable. The calcium sulfate residue of these processes, usually containing less than 1% of unreacted CaFa, is discharged and discarded.

It is also advisable to add small amounts of acid-grade fiuorspar from time to time to the calcium fluoride precipitate from Step A used in this step, to make up for mechanical and other losses in the recycling of reagents through this process. Such losses can be kept below 5% (of the total charge of CaFz used) per cycle.

STEP D The aqueous hydrofluoric acid solution (containing 5% to 50% HF) obtained in Step C is now reacted with a member of the group consisting of titanium dioxide, hydrated titanium dioxide and titanic acid, in stoichiometric proportions as is required for the formation of fluotitanic acid.

The titanium compound used may be any suitably pure compound of tetravalent titanium and oxygen. Metallurgical titanium dioxide or rutile may be used. An ideal source of titanium is the hydrated TiOz (or titanic acid) obtained by the hydrolysis of the titanic sulfate in the widely practiced Washburn process (U. S. Patent 1,889,- 027 (1933); British Patent 288,569 (1927)). The titanium compound dissolves readily in the hydrofluoric acid solution, especially on heating for a short period. The hydrated titania dissolves more readily than does the anhydrous or crystalline titani.

The resultant solution of fluotitanic acid is now reacted with a member of the group consisting of the hydroxides, carbonates or bicarbonates of the alkali metals, ac-

cording to the equation:

The alkali metal carbonate solutions obtained as the filtrate in Step B are ideally suited for this neutralization. When these are so used, the carbon dioxide evolved during the neutralization may be used to etfect the carbonation in Step B. However, this process is not limited to the use of the filtrate of Step B in such a manner. A fresh solution of alkali may be employed.

There is thus obtained an aqueous solution containing alkali metal fluotitanate, from which the salt crystallizes on cooling. The most satisfactory recovery is obtained with potassium fluotitanate which is soluble in water to the extent of 1.28% at 20 C. and 0.75% at 5 C. On cooling, almost all of the KaTiFe crystallizes out as the monohydrate. Lithium fluotitanate (LiaTiFs.2H20) and sodium fluotitanate (NazTiFs) are considerably more soluble, and may precipitate only incompletely on cooling. It may be necessary to concentrate solutions of these salts to obtain adequate recovery.

After filtering oil the alkali metalv fluotitanate, the aqueous filtrate may then be divided into two portions. The first portion is returned to the process for use in masses Step. A as the aqueous medium for the preparation of" themilk of lime slurry. The other portion is returned to the process for u e Step C as the aqueous medium for the absorption of the; HF gas in the preparation of filtrate from Step D', which is a solution of alkali metal fluotitanate saturatedat the temperature of the filtration.

The following example is given to define and to illus trate this invention but innoway' to limit it to reagents, proportions and conditions describedther'ein. Obvious modifications will occur to any person skilled in the art;

All proportions given are parts by weight.

Example A magnesia-lined crucible is charged with 68 parts of molten aluminum metal and 240 parts of anhydrous potassium fluotitanate is added. The mixture is placed in an induction furnace and slowly heated, with agitation, until the reaction is complete and the reaction mixture has obtained a temperature of about 1500 C. The molten reaction mixture is maintained near this temperature for about 15 minutes, and the molten slag (comprising an equimolecular mixture of KsAlFs and AlFs) is then carefully decanted from the regulus of molten titanium-aluminum alloy. The molten alloyjs cooled slowly to room temperature. There is thus obtained about 78.0-79.0 parts of an alloy containing about 60%."titanium and 40% aluminum.

The molten slag salt mixture,'containing 172.2 parts of KsAlFs (0.67 mole) and 56.0 parts of AlFa (0.67

mole) is cooled rapidly and solidified. The solid is comminuted and added to a slurry of 171 parts of lime (C210) (3 moles) in 2000 parts of water. (Instead of water in succeeding runs, the filtrate from the final precipitate of KzTiFs may be used here.) The reaction mixture is heated at 95-l00 C. with good agitation for an hour, or until precipitation of CaFz is complete. The precipitated calcium fluoride is then filtered off, washed on the fiiterpress with a small amount of hot water, and the 6 now the solution of 138 parts; of KiCOs (1 mole) in 2100 parts ofiwat'er reseived'from the preceding step. Carbon dioxide (44 parts) will be evolved, and may be piped off and used to carbonate a s'ucceedingbatch of potassium aluminates solution. Oncooling' to 5-10 C., a copious precipitate of K2TiFe.H2O settles out. This is filtered off, anddehydrated drying ata temperature of 150200 C. There isthus obtained 210- 215 PaIIs Of K2TiFs which are returned, with make-up to the firstv stepof the process. Theflfilt'rate from the KzTiFsHzO precipitate (about 3200 parts of solution containing about parts of KzTiFs) is divided. Part is used to makeup thelime slurry for reaction with the KsAlFe-AlFs salt mixture (q. v. suprayand the re mainder is used to absorb the. HF g as' (q; v. supra). By this recycling" of'the filtrate; the'yield of KzTiFs (anhydrous basis) in succeeding batches may be brought combined filtrate and washings are combined. The filtercake is pressed as free of water as possible.

The combined filtrate and washings from the preceding step are now carbonated at atmospheric temperature, while still hot (i. e. at 90 C.) until a total of 44 parts of carbon dioxide has been absorbed. The precipitated aluminum hydroxide is filtered off, washed on the filterpress with a small amount of hot water, pressed as free of water as possible, and is then'calcined at 900"- 1100" C. for conversion to alpha-alumina. From 62 to 'parts of alumina are thus'recoverable. The filtrate and washings from the AI(QH)3 precipitate, comprising a solution of 138 parts of K2CO3 in about 2100, parts of water, are retained for subsequent use.

The calcium fluoride filtercake obtained above (containing about 234 parts of CaFz (3 moles) is mixed with 425 parts of 66 B. sulfuric acid (4'moles) and heated in a rotary kiln, or by any of the methods well known in the art, to generate hydrogen fluoride gas. The HP gas evolved (120 parts) is absorbed in 1080 parts of water to yield 1200 parts of a 10% w./w. hydrofluoric acid solution. (After the first run, the filtrate from the final precipitate of KaTiFs may be used in place of water to make up this hydrofluoric acid solution. it is also advisable to add to each succeeding batch of CaFg filtercake, about 12 parts of acid-grade fluorspar to compensate for mechanical and other'losses.)

To the 1200 parts of 10% HF solution (6 moles), add now 80.0 parts oftitanium dioxide (1 mole) and heat, with agitation, until the TiOz has dissolved. Add 7 to 240 parts per cycle.

A raw materials balance for this process follows:

78.0-79.0 parts of 60% yield Ti/40% Al alloy 62-65 parts of alumina Having described my invention, what I claim and desire to protect by Letters Patent is:

1. A cyclic process for the manufacture of titaniumaluminum alloys and the regeneration of the intermediates of said process which comprises the steps of: (a) reacting an alkali metal fluotitanate with metallic aluminum in stoichiometric excess at advanced temperatures to obtain the said titanium-aluminum alloy and a byproduct mixture of alkali metal fluoaluminate and aluminum fluoride, and thereafter separating said alloy from said salt mixture; (b) reacting the mixture of alkali metal fluoaluminate and aluminum fluoride, in an aqueous medium, with lime in quantity sufficient to form a precipitate of calcium fluoride and a solution of alkali metal aluminates, and separating said precipitate from said solution; (0) carbonating the alkali metal aluminates solution with a carbon dioxide-containing gas to form a precipitate of aluminum hydroxide and a solution of alkali metal carbonates, and separating said precipitate from said solution; (cl) reacting the calcium fluoride obtained in step (b) with sulfuric acid at advanced tembonates of the alkali metals, recovering the resultant al- -kali metal fiuotitanate and returning the same to the first step of the process. s

2. The process of claim 1 for the manufacture of titanium aluminum alloys containing from 0.1% to of titanium.

v 3. The process of claim 1 where from 3815 grams to47.9 kilograms of metallic aluminum is reacted with.

each gram-mole of alkali metal fiuotitanate.

4. The process of claim 1 'where the filtrate from the precipitate of alkali metal fluotitanateis used at least in part as the aqueous medium for the reaction of the alkali metal fluoaluminate-aluminum fluoride with' the limeinstep (b). 1

5. The process of claim 1 Where the filtrate from the precipitate of alkali metal fluotitanate is used at least in part as the aqueous medium for the absorption of the hydrogen fluoride gas in step (d).

6. The process of claim 1 where the filtrate fromstep (c) containing alkali metal carbonates is employed to neutralize the fluotitanic acid in step (e). V

7. The process of claim 1 where the carbon'dioxide evolved during the reaction of fluotitanic acid with an arsnsaeialkali metal carbonate in step (e) is employed to carbonate the alkali metal aluminates solution in step (c).

8. The process of claim 1 where the alkali metal fluotL tanate is potassium fiuotitanate.

9. The process of claim 1 where the alkali metal fluotitanate is sodium fiuotitanate.

10. The process of claim 1 where the alkali metal fluotitanate is lithium fluotitanate.

11. The process of claim 1 where the reaction of the alkali metal fiuotitanate and metallic aluminum is effected within a temperature range of 660 C. to 1800 C.

12. The process of claim 1 where the reaction mixture of the alkali metal fiuotitanate and metallic aluminum is brought to a terminal temperature within the range of 1100 C. to 1750 C.

13. The process of claim 1 where the reaction mixture of the alkali metal fluotitanate and metallic aluminum is brought to within a terminal temperature range at which both the end-product regulus of titanium-aluminum alloyv and by-product slag are in the molten state.

References Cited in the file of this patent UNITED STATES PATENTS Marcien Nov. 15, 1927 OTHER REFERENCES 

1. A CYCLIC PROCESS FOR THE MANUFACTURE OF TITANIUMALUMINUM ALLOYS AND THE REGENERATION OF THE INTERMEDIATES OF SAID PROCESS WHICH COMPRISES THE STEPS OF: (A) REACTING AN ALKALI METAL FLUOTITANATE WITH METALLIC ALUMINUM IN STOICHOMETRIC EXCESS AT ADVANCED TEMPERATURES TO OBTAIN THE SAID TITANIUM-ALUMINUM ALLOY AND A BYPRODUCT MIXTURE OF ALKALI METAL FLUOALUMINATE AND ALUMNINUM FLUORIDE, AND THEREAFTER SEPARATING SAID ALLOY FROM SAID SALT MIXTURE; (B) REACTING THE MIXTURE OF ALKALI METAL FLUOALUMINATE AND ALUMINUM FLUORIDE, IN AN AQUEOUS MEDIUM, WITH LIME IN QUANTITY SUFFICIENT TO FORM A PRECIPITATE OF CALCIUM FLUORIDE AND A SOLUTION OF ALKALI METAL ALUMINATES, AND SEPARATING SAID PRECIPITATE FROM SAID SOLUTION; (C) CARBONATING THE ALKALI METAL ALUMINATES SOLUTION WITH A CARBON DIOXIDE-CONTAINING GAS TO FORM A PRECIPITATE OF ALUMINUM HYDROXIDE AND A SOLUTION OF ALKALI METAL CARBONATES, AND SEPARATING SAID PRECIPITATE FROM SAID SOLUTION: (D) REACTING THE CALCIUM FLUORIDE OBTAINED IN STEP (B) WITH SULFURIC ACID AT ADVANCED TEMPERATURES TO FORM HYDROGEN FLUORIDE GAS, ABSORBING SAID GAS IN AN AQUEOUS MEDIUM AND REACTING THE RESULTANT SOLUTION OF HYDROFLUORIC ACID WITH A MEMBER OF THE GROUP CONSISTING OF TITANIUM DIOXIDE, HYDRATED TITANIUM DIOXIDE AND TITANIC ACID, WHEREBY AN AQUEOUS SOLUTION OF FLUOTITANIC ACID (H2TIF6) IS OBTAINED; AND (E) NEUTRALIZING THE FLUOTITANIC ACID WITH A MEMBER OF THE GROUP CONSISTING OF THE HYDROXIDES, CARBONATES AND THE BICARBONATES OF THE ALKALI METALS, RECOVERING THE RESULTANT ALKALI METAL FLUOTITANATE AND RETURNING THE SAME TO THE FIRST STEP OF THE PROCESS. 